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Stream Drainage Patterns · PlanetGeo: The Geology Podcast

0:03
SPEAKER_01: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
0:14
SPEAKER_01: Scared the shit out of Watson again.
0:16
SPEAKER_01: You're okay, though.
0:17
SPEAKER_00: You're okay.
0:20
SPEAKER_00: Skittish dog.
0:21
SPEAKER_00: See, that's funny because my dog, Tubbs, doesn't hear a thing.
0:25
SPEAKER_00: He can't hear anything.
0:27
SPEAKER_00: So yeah, me clapping is not gonna startle my dog.
0:32
SPEAKER_00: Hi, Chris.
0:33
SPEAKER_00: Hey, how you doing?
0:34
SPEAKER_00: I'm good.
0:35
SPEAKER_00: You?
0:36
SPEAKER_00: I am great.
0:37
SPEAKER_00: The weather is beautiful.
0:38
SPEAKER_01: I I'm good.
0:40
SPEAKER_01: You told me the other day that you think you're in the wrong calling.
0:44
SPEAKER_01: That you've you've found your new calling.
0:46
SPEAKER_01: You found your new passion.
0:48
SPEAKER_00: I did.
0:49
SPEAKER_00: I believe everybody is good at something, right?
0:52
SPEAKER_00: Like everybody is.
0:53
SPEAKER_00: And I found out what I'm really good at yesterday, actually.
0:56
SPEAKER_00: I rented a stump grinder, had a bunch of stumps, like a ridiculous amount of stumps.
1:03
SPEAKER_00: And I found out that I'm really, really talented at grinding stumps out.
1:08
SPEAKER_01: Okay.
1:09
SPEAKER_01: If you need your stumps ground down out there, 1-800 bullheist is the number to call, and uh that'll get you a stump grinder.
1:16
SPEAKER_01: He comes cheap.
1:17
SPEAKER_01: Oh, I'm not cheap.
1:18
SPEAKER_01: I am not cheap labor.
1:20
SPEAKER_01: Nope.
1:20
SPEAKER_01: Um Chris, this is your topic.
1:23
SPEAKER_01: This is well, this is one you pitch to me at least.
1:26
SPEAKER_01: Um I don't know this wasn't a hard sell, I don't think.
1:29
SPEAKER_01: This is uh pretty good topic.
1:31
SPEAKER_01: No, I didn't feel like it was a we we didn't quite get close to breaking up, I don't think.
1:35
SPEAKER_01: Do you did you feel like I was hard to uh hard to pitch on this one?
1:38
SPEAKER_00: No, I just didn't think that you were overly I didn't think you were adequately enthused about it, but that's typical.
1:43
SPEAKER_00: Whenever I come to you with an idea, you you just kind of like you you poo-poo it.
1:47
SPEAKER_00: You you know, and I I don't really appreciate that.
1:49
SPEAKER_01: No, no, no.
1:50
SPEAKER_01: You just want a yes man.
1:51
SPEAKER_01: You just want somebody over here, just a sycophant, who just says, yes, Mr.
1:54
SPEAKER_01: Bois, we can do whatever you want.
1:56
SPEAKER_01: You're the best, Mr.
1:57
SPEAKER_01: Boyes.
1:57
SPEAKER_01: That's what you want to do.
2:00
SPEAKER_00: Well, no, I just uh when I come up with good ideas, I expect that to be acknowledged, and you rarely come across with positive reinforcement.
2:08
SPEAKER_00: I need I need more of that.
2:10
SPEAKER_01: You do you do, you need some coaxing.
2:12
SPEAKER_01: That ego is uh, you know, it's a fragile ego over there sitting in the bull eyes also.
2:17
SPEAKER_01: Hey, let's get to it.
2:19
SPEAKER_01: Stream drainage patterns.
2:20
SPEAKER_01: This is this is a cool topic.
2:22
SPEAKER_01: This is something you cover in your geology 101 intro to geoscience class.
2:26
SPEAKER_01: This is one I cover.
2:28
SPEAKER_01: I obviously, as we've talked about before, I cover it less than you do.
2:31
SPEAKER_01: Like I just don't have the time, so I don't spend a lot of time in it.
2:34
SPEAKER_01: I do cover the drainage pattern that we have in Pennsylvania, though.
2:37
SPEAKER_01: But it's a really important concept, and again, it's one of these things that just shows that geology is all around us, right, Chris?
2:43
SPEAKER_01: I mean, it's a cool lens to put on your life, I think.
2:47
SPEAKER_00: I agree.
2:48
SPEAKER_00: You know, if you look at a map, okay, and you just blot out everything else in front of you when you're looking at this map, and you just focus on the streams themselves, so the major rivers and then all of its tributaries.
3:00
SPEAKER_00: The pattern that develops before your eyes, then, is it's not a random thing.
3:05
SPEAKER_00: There is a definite pattern to the stream development there.
3:10
SPEAKER_00: And like you just said, the geology is all around us, and so the pattern that streams develop is determined by the geology exposed at the surface.
3:21
SPEAKER_00: Yes, and that's a cool realization.
3:23
SPEAKER_01: All about geology, it's all governed by geology, right?
3:26
SPEAKER_01: And actually, we can relate these, these relate to a couple different things.
3:31
SPEAKER_01: They're controlled by well, really what we're talking about is a pattern of erosion because that's where the streams go.
3:37
SPEAKER_01: The streams are doing erosion, and so the stream pattern is really fundamentally a pattern of erosion, and so it's controlled by the rock types underneath of the region, but also the structure of the rock types.
3:49
SPEAKER_01: So there's a couple different things that are going into this.
3:52
SPEAKER_01: And I think, Chris, let me just back up and say we've talked about meanders recently and how plants affect meanders.
3:57
SPEAKER_01: We're zooming kind of back out a little bit more, and we're looking at the drainage network, so how a bunch of different rivers interact in a river system.
4:06
SPEAKER_01: And we call that like a drainage network, and the sort of unit of interest here is a drainage basin.
4:11
SPEAKER_01: So maybe, Chris, what we could do is define that first and sort of get everybody thinking about the scale of the map that we're looking at here.
4:19
SPEAKER_01: Like if you look at a map on your a topo map and draw out the rivers, like you said, what's the scale we're dealing with?
4:25
SPEAKER_00: Can you well that was a very interesting way of framing the question?
4:28
SPEAKER_00: I think.
4:29
SPEAKER_00: Do I get an award for the world's longest question there?
4:33
SPEAKER_00: Do you want to know what a drainage basin is?
4:35
SPEAKER_00: Is that what you're asking me to do?
4:36
SPEAKER_00: That's what I'm getting at a little bit.
4:37
SPEAKER_00: Yeah.
4:38
SPEAKER_00: Oh my gosh.
4:39
SPEAKER_00: Okay.
4:40
SPEAKER_00: Just you know what?
4:40
SPEAKER_00: Just start doing better.
4:42
SPEAKER_00: Okay.
4:42
SPEAKER_00: I need you to do better.
4:43
SPEAKER_00: I'll pick it up.
4:44
SPEAKER_00: Okay.
4:45
SPEAKER_00: So anyway, all right.
4:46
SPEAKER_00: A drainage basin, Dr.
4:48
SPEAKER_00: Rymank.
4:49
SPEAKER_00: Um, is a drainage basin and watersheds are really the same thing?
4:54
SPEAKER_00: So basically, it's an the area that we're looking at that is drained by a river and all of its tributaries.
5:00
SPEAKER_00: That's what a drainage basin is.
5:02
SPEAKER_00: So here, let me let me give some examples, right?
5:04
SPEAKER_00: I live in in you know, southwest Michigan, and the the main river that runs through my area is called the Grand River.
5:12
SPEAKER_01: Oh, the Grand Rapid.
5:13
SPEAKER_00: Runs through Grand Rapids, yep, the Grand, right?
5:15
SPEAKER_01: We were just, Chris, at our conference, we were just looking over the Grand River.
5:18
SPEAKER_01: We went and had a beer right near the Grand River.
5:20
SPEAKER_01: It's it's nice down there in Grand Rapids.
5:23
SPEAKER_00: It is.
5:23
SPEAKER_00: It is so nice, actually.
5:25
SPEAKER_00: It really is.
5:25
SPEAKER_00: Yeah, so the Grand River is the main river.
5:28
SPEAKER_00: So we call this the Grand River watershed.
5:30
SPEAKER_00: So it's that river and all of the other tributaries in the area that empty into the Grand.
5:36
SPEAKER_00: But then we live in, if we back off from this a little bit and take a broader or farther away view, we live in the Great Lakes drainage basin or the Great Lakes watershed.
5:47
SPEAKER_00: And then they're drained by the St.
5:49
SPEAKER_00: Lawrence River and it goes off into the North Atlantic.
5:52
SPEAKER_00: And you know, so you have the biggest river drainage basin in the United States is the Mississippi River drainage basin.
6:00
SPEAKER_00: This covers uh an unbelievably massive amount of land, and it all runs through New Orleans and out in you and I were there last year.
6:10
SPEAKER_00: We both we had again, once again, Jesse and Chris having a beer looking at the Mississippi River.
6:16
SPEAKER_01: Put us near a river and we're gonna look for a beer.
6:19
SPEAKER_01: Um this this pattern, this stream drainage pattern characteristic occurs at a variety of scales, right?
6:25
SPEAKER_01: And and you described that there's different drainage basins, different divides, depending on how you break it up.
6:29
SPEAKER_01: You could have a little stream drainage pattern that exists on your driveway, Chris, versus in your grass next door.
6:37
SPEAKER_01: And there could be what's called a divide.
6:39
SPEAKER_01: The way to think about a divide is it's breaking apart drainage basins.
6:43
SPEAKER_01: And so if a water droplet falls somewhere on the ground, where does it end up going?
6:47
SPEAKER_01: Which river does it end up going in?
6:49
SPEAKER_01: And often people have heard of continental divides, which is water flows to the Pacific or the Atlantic or the Gulf of Mexico or the Arctic.
6:57
SPEAKER_01: That's a huge divide.
6:59
SPEAKER_01: There's also pretty small divides that divide the grand rivers.
7:02
SPEAKER_00: Hold on, can I interrupt you a second?
7:04
SPEAKER_00: Because I think the continental divide, the idea of the continental divide, is such a cool thing.
7:09
SPEAKER_00: We're talking about an imaginary line.
7:12
SPEAKER_00: Literally, it's a line that separates where the water goes.
7:17
SPEAKER_00: Water that hits on one side of that imaginary line goes to the Atlantic Ocean.
7:20
SPEAKER_00: Water that hits on the other side of that line is gonna go to the Pacific Ocean.
7:24
SPEAKER_00: That's really a cool thing, right?
7:25
SPEAKER_00: So if you take uh an Algene bottle full of water and you're on that continental divide and you pour the water on that imaginary line, some of the water's gonna go in opposite directions.
7:36
SPEAKER_00: You know, some of the water's gonna go to the Atlantic and some's going to the Pacific.
7:39
SPEAKER_00: That's power right there, Jesse.
7:41
SPEAKER_00: Like it's you're dumping water and helping both oceans at the same time.
7:45
SPEAKER_00: I I I think about that.
7:47
SPEAKER_01: Yeah, you you sit there and think, wow, I'm so strong and powerful, I have so much influence.
7:52
SPEAKER_01: And then you look at the ocean, you think, oh, that's not very much that I added at all.
7:56
SPEAKER_01: But you know, the peak of a roof is a divide.
7:59
SPEAKER_01: Yep, that's right.
8:00
SPEAKER_00: You know, think about it that way.
8:01
SPEAKER_00: Water that hits on one side of your roof is gonna go one direction, on the other side, it's going the other direction.
8:06
SPEAKER_00: That's what a divide looks like.
8:07
SPEAKER_00: So we have these local divides, continental divides.
8:10
SPEAKER_00: A local divide here in southwest Michigan is this imaginary line.
8:15
SPEAKER_00: It's a topographic high that separates, let's say, the Kalamazoo River from the Grand River.
8:21
SPEAKER_00: That's a local divide.
8:23
SPEAKER_01: So we have a lot of these in Pennsylvania.
8:25
SPEAKER_01: We have a lot of ridges that divide these little streams.
8:28
SPEAKER_01: You can be in the Penn Creek watershed or the Spring Creek watershed, right?
8:30
SPEAKER_01: And these are very different, very localized things.
8:33
SPEAKER_01: What we're talking about today, though, really, is the pattern of stream drainage.
8:38
SPEAKER_01: And these occur in regions, these are kind of intermediate.
8:41
SPEAKER_01: There will be in a continental scale watershed, in the Mississippi watershed, there's going to be a bunch of different stream drainage patterns.
8:49
SPEAKER_01: They can be fairly local.
8:51
SPEAKER_01: They're kind of, like we said, governed by the geology.
8:53
SPEAKER_01: So anytime you have consistent geology in a region, you'll often have a consistent stream drainage pattern.
8:59
SPEAKER_01: And the way to think about this is this is the way that the streams, the different categories of streams interact with each other.
9:05
SPEAKER_01: The shape of if you just removed everything from the topo map, Chris, and just had the blue lines of rivers there, what is that shape?
9:13
SPEAKER_01: What does the pattern that those things make?
9:15
SPEAKER_01: And I want to just give two definitions, and Chris, then I want us to like give an overview of what we're going to cover here.
9:21
SPEAKER_01: We're going to talk about mainstreams and tributaries.
9:24
SPEAKER_01: And really, tributaries is a river that flows into another river.
9:27
SPEAKER_01: So it's the smaller one that flows into the bigger one, and the main stream is the big one.
9:32
SPEAKER_00: And you know, a mainstream is the way I say this to my students is a tributary contributes its water to the mainstream.
9:39
SPEAKER_01: Perfect.
9:39
SPEAKER_01: And if you have two equally sized streams coming together, they're often not perfectly equal.
9:44
SPEAKER_01: There'll be one bigger, and that one will be the mainstream, and then the other one will be the tributary.
9:48
SPEAKER_01: And a mainstream can also be a tributary and often will be a tributary as a big river flows into an even bigger river.
9:55
SPEAKER_01: The Missouri River flows into the Mississippi River, right?
9:57
SPEAKER_01: And then becomes a tributary.
9:59
SPEAKER_01: So that's the we're going to talk a lot about those two words.
10:02
SPEAKER_01: And so I kind of wanted to define those up front.
10:04
SPEAKER_01: So what are the patterns?
10:05
SPEAKER_01: And Chris, what do you cover in your class?
10:07
SPEAKER_01: I'll be curious to know uh how it compares to what I cover.
10:10
SPEAKER_00: Yeah, sure.
10:10
SPEAKER_00: We're first of all, I want to just mention the the drainage patterns that we're gonna cover.
10:14
SPEAKER_00: It's not a comprehensive list.
10:16
SPEAKER_00: We're doing the top five here, basically, or what I think of as the top five drainage patterns.
10:22
SPEAKER_00: So we're gonna cover dendritic drainage pattern, trellis, annular, rectangular, and radial drainage patterns.
10:30
SPEAKER_00: But we're focusing on what do these patterns look like?
10:33
SPEAKER_00: And we're gonna do our best to paint a visual in your head of what these things each look like.
10:38
SPEAKER_00: Like the focus of this is what's the geology then?
10:42
SPEAKER_00: What determines that drainage pattern?
10:44
SPEAKER_00: Because that's exactly what happens.
10:46
SPEAKER_00: So we're gonna focus on those.
10:48
SPEAKER_01: And that, Chris, let me interrupt there.
10:49
SPEAKER_01: That is a really, really cool thing and why this is so interesting and powerful is you can look at the stream pattern.
10:55
SPEAKER_01: You can just look at a map and you can infer what the geology is at a rough scale.
10:59
SPEAKER_01: You can infer the pattern of geology underneath of that land, even without the topographic map.
11:05
SPEAKER_01: You could just look at the streams, not any topography at all, just the stream pattern, and you could say, Oh, I think this geology is roughly X, Y, or Z.
11:14
SPEAKER_00: I'm gonna interrupt you just one second before we jump into the first one, which is dendritic, is that this is one of the things that that my students struggle with, perhaps.
11:22
SPEAKER_00: Well, I don't know if I want to say the most, but they struggle with it because when Dr.
11:26
SPEAKER_00: Maddox comes in and gives them their exam, part of that is a practical topographic map exam.
11:31
SPEAKER_00: So he'll throw a map out in front of him and say, all right, what is the drainage pattern below you on this map?
11:38
SPEAKER_00: And what I tell them to do is you have to blot out everything and just focus on the blue lines because those are the rivers.
11:46
SPEAKER_00: And I'll tell him, you know, just pick up a dry erase marker and draw on the map, trace the rivers, and then a pattern develops before you, and that pattern, there's your answer.
11:55
SPEAKER_01: So yeah, super easy.
11:57
SPEAKER_01: So, Chris, well, dendritic.
11:59
SPEAKER_01: You said dendritic is the the first one here, right?
12:01
SPEAKER_01: And this is by far the most common.
12:03
SPEAKER_01: And I think this is some of these will become hard to visualize, but this one's not.
12:08
SPEAKER_01: This is just a tree, and you can either think of a branching of a tree, like the tree branches going up, or the roots going down.
12:15
SPEAKER_01: Either one kind of gets you the visual that we're after.
12:18
SPEAKER_01: Let's go with the tree going up, though.
12:20
SPEAKER_01: If you imagine water flowing from the tips of the tree down to the trunk, that's what we're envisioning.
12:27
SPEAKER_01: So a bunch of little branches, little stems that merge and become small branches that then merge and become big branches, that then merge to the trunk and become one singular trunk.
12:37
SPEAKER_01: And they're all kind of pointing not exactly in the same direction, but generally in the same direction.
12:43
SPEAKER_01: They're kind of joining with like V shapes, they're never really intersecting at 90 degree angles, not frequently, at least.
12:49
SPEAKER_01: They're mostly joining with like kind of V shapes, if that makes sense.
12:53
SPEAKER_01: So that's the way I think of dendritic.
12:55
SPEAKER_00: That's right.
12:56
SPEAKER_00: You know, I think the name actually is derived from the biological sense, and I hate to say that, but I think it's true.
13:02
SPEAKER_00: Yeah.
13:03
SPEAKER_00: You know, these dendrites that you get in nerve endings, right?
13:07
SPEAKER_00: These extensions on nerve endings and so on.
13:10
SPEAKER_00: Because that's what a dendritic drainage pattern looks like.
13:13
SPEAKER_00: It resembles the dendrites that you learned about in biology 101.
13:18
SPEAKER_00: So, yeah, I think of it too as you said a branching tree, which is a great analogy, and the flow is down to the trunk, right?
13:25
SPEAKER_00: Or think about holding a maple leaf in your hand.
13:29
SPEAKER_00: And you look at the veins inside the leaf, and those veins come down to the stem.
13:34
SPEAKER_00: That's what a dendritic drainage pattern looks like as well.
13:37
SPEAKER_00: So I think I hope we've painted a visual for you in this of what dendritic drainage patterns look like.
13:44
SPEAKER_00: So, Jesse, let's get into the geology then.
13:47
SPEAKER_00: What determines it?
13:48
SPEAKER_00: What causes it?
13:49
SPEAKER_01: It's kind of simple, actually.
13:50
SPEAKER_01: It's just uniform geology.
13:52
SPEAKER_01: This happens, this occurs when the geology is basically the same underneath of the entire drainage area.
14:00
SPEAKER_01: And the way I kind of think about this, Chris, is think about like a gravel driveway.
14:05
SPEAKER_01: Your gravel driveway, when it rains really hard, you kind of get this dendritic pattern forming.
14:11
SPEAKER_01: You'll get little tiny rivulets that merge together, and eventually at the bottom of the driveway, you'll have kind of a bigger sort of stream, mini stream coming out there.
14:19
SPEAKER_01: It forms that way because the entire gravel driveway is more or less the same.
14:24
SPEAKER_01: There's no big, you know, breaks in it.
14:25
SPEAKER_01: If you had like asphalt, then gravel, there'd be a big difference in how the water pattern behaved.
14:30
SPEAKER_01: But dendritic is sort of governed by the physics, not the geology, because the geology is all kind of the same.
14:36
SPEAKER_01: That's the way I sort of think about it.
14:38
SPEAKER_00: That's right.
14:39
SPEAKER_00: Because it's a homogeneous material at the surface, right?
14:42
SPEAKER_00: Erosion can happen equally in any direction.
14:45
SPEAKER_00: Right.
14:45
SPEAKER_00: And so that's kind of what governs then a dendritic drainage pattern.
14:48
SPEAKER_00: But I do have to ask you, Jesse, have you ever been to my house?
14:51
SPEAKER_00: Have you been to my house?
14:53
SPEAKER_00: I have been to your house, yeah.
14:54
SPEAKER_00: Well, then why would you say I have a gravel driveway?
14:57
SPEAKER_00: Well, sorry, I don't understand.
14:58
SPEAKER_01: I meant your road.
14:59
SPEAKER_01: Your road, your gravel road that you drive.
15:01
SPEAKER_00: Oh my gosh.
15:03
SPEAKER_00: All right.
15:03
SPEAKER_00: So anyway, working with you is so difficult.
15:08
SPEAKER_00: It's very difficult.
15:09
SPEAKER_00: So examples of the this homogenous rock type, you uh if you have granite at the surface, like the Canadian Shield, right?
15:16
SPEAKER_00: Typified by this dendritic range pattern.
15:19
SPEAKER_00: Nice.
15:19
SPEAKER_00: This metamorphic uh one of our favorite rocks, nice.
15:22
SPEAKER_00: If if this is dominant at the surface, that's a range pattern.
15:25
SPEAKER_00: Flat sedimentary.
15:27
SPEAKER_00: Or in in my case, I live in Michigan and and we have this kind of glacial kitty litter all over the state.
15:33
SPEAKER_00: This, you know, two to five hundred feet of glacial debris, Michigan's dominated by a dendritic drainage pattern.
15:40
SPEAKER_01: Yeah, and it's fairly homogenous.
15:42
SPEAKER_01: And we mean homogenous on a sort of a general scale.
15:44
SPEAKER_01: If you look at a nice, a rock that's a gneiss, like obviously there's going to be weak parts and strong parts in a hand sample, but we're talking about at the scale of larger streams, right?
15:54
SPEAKER_01: So there's not a lot of texture to it or a lot of weak layers and strong layers.
15:59
SPEAKER_01: And I think it's important, Chris.
16:00
SPEAKER_01: I just want to double-click on flat sedimentary, because flat is the key part there.
16:04
SPEAKER_01: If you have one sandstone layer that's exposed at the surface, you'll get dendritic.
16:08
SPEAKER_00: Ooh, you get the Segway Award.
16:11
SPEAKER_00: Good one, right?
16:11
SPEAKER_00: Look at you go.
16:13
SPEAKER_01: Nice segue.
16:14
SPEAKER_01: Because that leads into the next one, number two on our stream drainage patterns is trellis.
16:20
SPEAKER_01: And this is, let me describe trellis first, Chris, because this is where I live in Pennsylvania.
16:25
SPEAKER_01: We have a trellis pattern.
16:27
SPEAKER_01: And a trellis pattern is, I think most people kind of can visualize what a trellis is, like a yard trellis, something in your garden, maybe trellis hanging over your patio or something like that.
16:38
SPEAKER_01: You have main branches that flow kind of parallel to one another with offshoot branches that connect into it at 90 degrees.
16:46
SPEAKER_01: So mainstream trunks flow parallel, tributaries come down and intersect those main trunks at 90 degree angles.
16:53
SPEAKER_01: And that's trellis.
16:55
SPEAKER_01: They kind of are this interconnected, they're mostly right angles.
16:58
SPEAKER_01: It's mostly right angles with main things.
17:00
SPEAKER_00: Let me interrupt you a second, Jesse.
17:01
SPEAKER_00: Is this the first one that you teach?
17:03
SPEAKER_01: I no, I actually build for this.
17:05
SPEAKER_01: I cover the other ones and then I end with this because it's like sort of like, okay, I'll list a couple and then end with the one that matters to them, and I can show them maps of it.
17:12
SPEAKER_01: So, but it all happens in about 20 minutes in a lecture.
17:16
SPEAKER_00: Okay, that's fast.
17:18
SPEAKER_00: That's some fast visualization right there.
17:20
SPEAKER_01: Yeah.
17:20
SPEAKER_01: Okay.
17:20
SPEAKER_01: So it looks like a garden trellis, and um that I guess I think I covered it there, right, Chris?
17:26
SPEAKER_01: So how it is.
17:27
SPEAKER_01: I think so.
17:27
SPEAKER_00: That's a good visual.
17:28
SPEAKER_00: I think everybody knows what a garden trellis looks like.
17:31
SPEAKER_00: That's what the river system looks like then.
17:33
SPEAKER_00: In like you said, Pennsylvania, and actually a lot of Appalachia, right?
17:36
SPEAKER_00: I mean, because what's the geology?
17:38
SPEAKER_00: The geology determines the pattern.
17:40
SPEAKER_00: Well, this is what you get when you don't have flat line sedimentary rocks, but instead you have folded sedimentary rocks.
17:48
SPEAKER_00: Exactly.
17:49
SPEAKER_00: What does this do?
17:50
SPEAKER_00: That's the question, right?
17:51
SPEAKER_00: When you take sedimentary rocks that were flat, you squish them in tectonics, and then they become folded kind of like rumpled carpeting, right?
18:01
SPEAKER_00: What's the result of that?
18:02
SPEAKER_00: What that results in is strong rock and weak rock exposed at the surface now because they're not flat line anymore.
18:11
SPEAKER_00: I don't have one uniform rock.
18:13
SPEAKER_00: I've got multiple rocks.
18:14
SPEAKER_00: Some of them are strong, like me, some of them are weak, like you.
18:18
SPEAKER_00: And that's so then what happens is what what what?
18:25
SPEAKER_00: That was a good analogy.
18:27
SPEAKER_01: You're funny, you're funny, you're funny today.
18:31
SPEAKER_00: Well, all right.
18:32
SPEAKER_00: So these rocks are parallel now at the surface, but they're not the same strength.
18:36
SPEAKER_00: And so basically now we just get into differential erosion, differential weathering and erosion.
18:41
SPEAKER_00: Strong rocks form ridges, weak rocks form valleys, and the main rivers flow down the valleys.
18:47
SPEAKER_01: Yeah, it's a really cool thing here in central Pennsylvania where we have we're in the folded sediments.
18:53
SPEAKER_01: We're in what's called the Ridge and Valley province, and it's all the folded sediments from Appalachia that have been folded back and forth and turned on edge.
19:00
SPEAKER_01: And all those folds have been squished together, turned on edge.
19:03
SPEAKER_01: And so in this part of Pennsylvania, the valley formers, the weak rocks are shales and actually limestones as well, because we get so much rain and it's slightly acidic, it kind of chemically erodes that stuff.
19:14
SPEAKER_01: The ridges are all quartzites.
19:16
SPEAKER_01: Yeah.
19:16
SPEAKER_01: Well, okay.
19:17
SPEAKER_01: The ridges are all quartzites for the most part.
19:20
SPEAKER_01: So what we have, and actually, this is I just found this out.
19:23
SPEAKER_01: I haven't confirmed this, but when you're driving through, you can often see like hawks love this area because wind will come and wind will hit the ridges and just kick up these updrafts.
19:33
SPEAKER_01: So hawks can just glide for miles.
19:35
SPEAKER_01: And I heard somebody told me, I haven't confirmed this, but that like the world glider record or something like that is in Pennsylvania.
19:43
SPEAKER_01: Somebody took a glider and went from Pennsylvania down the ridge and valley province all the way to the Carolinas and then back because there's one of these great updraft days, and you can just soar along a single ridge line for really, really long ways.
19:56
SPEAKER_01: And that's unbelievable.
19:58
SPEAKER_01: There's a river flowing in the valley, a main trunk flowing in the valley down that ridge with all the tributaries coming off of these two ridges, flowing straight downhill, hitting that trunk at 90 degree angles, and then flowing down the valley.
20:12
SPEAKER_01: That's what's happening.
20:13
SPEAKER_00: Very, very cool, Jesse.
20:14
SPEAKER_00: Um, I I did not know that either.
20:17
SPEAKER_00: That's that's awesome.
20:18
SPEAKER_00: Um, really cool about the hawks, too.
20:20
SPEAKER_01: Yeah, you can see them, they're they love it.
20:22
SPEAKER_01: They love it because they could just soar for so long.
20:24
SPEAKER_00: Yeah, let's but let's talk about what happens with these where the rivers flowing down the ridges into the valleys.
20:31
SPEAKER_00: Sometimes in some places, it's actually gonna cut a gap through those ridges, right?
20:37
SPEAKER_00: Well, what's happening then is as the river flows down over time, over time, over time, it's cutting this deeper and deeper valley and headward erosion is happening, and it's going to intersect eventually the course of another river on the opposite side of the ridge, and therefore cut a gap, what we call them water gaps, through these ridges.
21:00
SPEAKER_00: And so you do get those as well.
21:03
SPEAKER_01: For sure.
21:03
SPEAKER_01: And you can see that in the in the the drainage pattern.
21:06
SPEAKER_01: You know, the highway follows one of the main rivers through here because the river cut this gap through the ridges.
21:11
SPEAKER_01: So instead of the highway having to go up the ridge, down the ridge, up the ridge, down the ridge, it follows the river that cut the main rivers that cut through or follow these water gaps that have cut through the ridge lines and cut across that.
21:22
SPEAKER_01: But then branching away from that, the tributaries are this trellis structure that are flowing sort of straight through the valleys.
21:29
SPEAKER_01: All right.
21:30
SPEAKER_01: Does that cover trellis then?
21:31
SPEAKER_01: So trellis is again just tilted sediments.
21:33
SPEAKER_01: That's what's going on.
21:34
SPEAKER_01: Tilted sediments, they're parallel, strong and weak layers, and we get this trellis pattern.
21:39
SPEAKER_00: Okay.
21:40
SPEAKER_00: Well, that actually is a very nice segue into our third type of drainage pattern, which is called annular.
21:45
SPEAKER_00: Now, you were wondering why I put this together in this order.
21:50
SPEAKER_00: This is really the reason, is because annular, the pattern that you get is very similar to the reason why trellis is the pattern you get in folded regions.
21:59
SPEAKER_00: And annular.
22:00
SPEAKER_00: Annular drainage pattern is when you have streams that flow in incomplete circles.
22:05
SPEAKER_00: They try to flow in a circle, but it doesn't quite work out that way.
22:10
SPEAKER_00: So they're these like incomplete concentric circles.
22:15
SPEAKER_00: Okay, that's an annular drainage pattern.
22:17
SPEAKER_01: I think, Chris, the way the visual that makes some sense to me is it's kind of like spokes on a wheel, except the spokes are really small, and you have the spokes are all connected to each other, but not quite connected to each other.
22:30
SPEAKER_01: And so it's kind of like a trellis pattern, except the main branches are flowing not parallel to each other, but away from each other, if that makes sense.
22:39
SPEAKER_01: Um this is the hardest one for me to visualize.
22:42
SPEAKER_00: I think you confused me.
22:43
SPEAKER_00: Uh let me let me can I have another crack at this a second.
22:46
SPEAKER_00: Yeah.
22:47
SPEAKER_00: Yeah, go for it.
22:48
SPEAKER_00: Imagine, okay, draw a circle, okay, and then draw a bigger circle around the smaller circle.
22:54
SPEAKER_00: You're using a pencil, and you take an eraser then, and you you know, just make a little eraser, so you break up your circle a little bit.
23:02
SPEAKER_00: Okay.
23:02
SPEAKER_00: Now draw smaller lines going away from the circles, like at right angles to the circle.
23:10
SPEAKER_00: Okay, that's what a an annular drainage pattern looks like.
23:14
SPEAKER_00: So it's tr it's flowing these curved lines, right?
23:17
SPEAKER_01: Yep, that's a better description, Chris, because I think if you just the the incomplete circles, I think the thought is, well, where does the water go?
23:24
SPEAKER_01: Well, the water is kind of flowing ultimately radially away.
23:28
SPEAKER_01: So it is this concentric circle.
23:30
SPEAKER_01: The main trunks are actually flowing radially away, so there's maybe like four spokes, and then inside you have these incomplete circular patterns, these concentric rings of incomplete circles.
23:41
SPEAKER_00: And where do you get that?
23:43
SPEAKER_00: This is controlled by structural domes and structural basins.
23:47
SPEAKER_00: And I think one of the most famous examples of a structural dome, and we did this in a previous episode, the Black Hills of South Dakota, where Mount Rushmore is.
23:56
SPEAKER_00: Okay.
23:57
SPEAKER_00: So this is a destination for a lot of people every single summer.
24:00
SPEAKER_00: Okay.
24:02
SPEAKER_00: So why?
24:03
SPEAKER_00: Well, when you have a structural dome or a structural basin, you have quite often these sedimentary rocks that are no longer flat line anymore.
24:12
SPEAKER_00: And so it's the same reason with trellis.
24:15
SPEAKER_00: You have now strong rocks and weak rocks exposed at the surface, but structural domes and basins form this kind of bullseye pattern, right, Jesse?
24:25
SPEAKER_00: Exactly.
24:26
SPEAKER_00: So you have this bullseye pattern where we have this soft, weak, wimpy rock-like shale juxtaposed in a circle, okay, juxtaposed next to sandstones, limestones, sometimes quartzites, these tougher, more resistant rocks, right?
24:44
SPEAKER_00: And so these incomplete circles are gonna follow the valleys, the shale.
24:51
SPEAKER_00: And for the same reason why you get water gaps in a trellis drainage pattern, you get water flying off the ridges down into the valleys, and they'll cut gaps through those bullseye-formed ridges.
25:06
SPEAKER_00: And now you have the main rivers then flowing away from the circles.
25:11
SPEAKER_01: And I think, Chris, let me bring this back to the trellis pattern.
25:15
SPEAKER_01: If we go back to that hawk, you know, the hawk I was describing in Pennsylvania here, that can go from Pennsylvania down to the Carolinas just by coasting along that.
25:23
SPEAKER_01: You can't do that in a dome because it'd just be going in a circle, right?
25:26
SPEAKER_01: The hawk would just go in a circle if it was trying to follow the same ridge.
25:29
SPEAKER_01: And the water does that too.
25:31
SPEAKER_01: So the water can't just go in a circle.
25:32
SPEAKER_01: And this is a game I always try and play when I'm thinking about drainage pattern evolution is what happens if I just cut off the main branches?
25:41
SPEAKER_01: The water would just fill up, right?
25:43
SPEAKER_01: The the water ultimately has to go somewhere.
25:45
SPEAKER_01: So it can't just fill up this circular ring.
25:48
SPEAKER_01: It'll break out somewhere and it'll cut through the ridge, and then that's a drainage network outlet.
25:53
SPEAKER_01: And so that instigates the sort of radial pattern of getting water out of this circular ring that it would just get caught in this loop over and over and over, right?
26:02
SPEAKER_01: It's got to break out of that at some point.
26:04
SPEAKER_01: So that's how we have this annular pattern.
26:07
SPEAKER_01: But Chris, this brings up an interesting question, which is you live in Michigan.
26:11
SPEAKER_01: I'm from Michigan.
26:12
SPEAKER_01: Michigan is a structural basin.
26:15
SPEAKER_01: You talked about Michigan having a dendritic pattern.
26:18
SPEAKER_01: Why does it not have an annular pattern?
26:19
SPEAKER_01: And I and and I probably I don't remember learning about the drainage patterns of Michigan.
26:25
SPEAKER_01: It's been a long time.
26:26
SPEAKER_01: Well, that hurt right there.
26:28
SPEAKER_00: That really hurt.
26:30
SPEAKER_01: I do remember a lot of what you say, but not everything.
26:32
SPEAKER_01: I'm sorry to say.
26:34
SPEAKER_00: Yeah, this is actually one of the most common questions that I get when I start talking about drainage patterns because they already know that we live in a structural basin.
26:42
SPEAKER_00: And so I'll start the whole thing off by saying, What do you think?
26:45
SPEAKER_00: Okay, here's here are the drainage patterns.
26:47
SPEAKER_00: What do you think Michigan has then?
26:49
SPEAKER_00: And they almost always right away say we have an annular drainage pattern then, because we live in a structural basin.
26:56
SPEAKER_00: And I'm like, Well, no, we don't.
26:59
SPEAKER_00: And the reason for it is is kind of cool and kind of simple.
27:02
SPEAKER_00: Above our rocks that are exposed in this bullseye kind of pattern is hundreds of feet of glacial till.
27:11
SPEAKER_00: This sediment that was dropped off by the glaciers during at the end of the last ice age.
27:17
SPEAKER_00: So our rock is relatively uniform at the surface.
27:21
SPEAKER_00: Now, given enough time, right?
27:23
SPEAKER_00: As the rivers remove away this glacial till, given geologic time, throw that into the mix now, then yeah, Michigan may develop as it gets rid of this glacial material.
27:33
SPEAKER_00: It may develop it the drainage pattern might change to annular.
27:36
SPEAKER_01: So it's really it's an important point.
27:37
SPEAKER_01: It's the rocks at the surface, the rocks that the water is interacting with that really drive this.
27:43
SPEAKER_01: Like the groundwater flow is a whole different ballgame.
27:46
SPEAKER_01: It's the water right at the surface that what that water sees is really what drives the stream drainage pattern.
27:52
SPEAKER_01: So let's move on, Chris, to radial.
27:55
SPEAKER_01: And this one I think is pretty dead simple.
27:57
SPEAKER_01: Radial is just like spokes on a wheel.
28:00
SPEAKER_01: Water is flowing sort of directly outwards from a central point, a central high point from spokes on a wheel.
28:06
SPEAKER_01: So, what does this tell us if we see a radial pattern?
28:08
SPEAKER_01: What does this tell us about the underlying geology?
28:11
SPEAKER_00: Right away, and the example that I always would use when talking about this is stratovolcanoes.
28:18
SPEAKER_00: You have this classic cone-shaped geologic massive feature at the surface, and it's steep slope too.
28:25
SPEAKER_00: And slope helps govern the pattern that you get as well.
28:28
SPEAKER_00: And because it's steep, the water's going to tend to flow in straight lines away from that central high point.
28:35
SPEAKER_00: And so that's the typical geology that determines a radial drainage pattern.
28:40
SPEAKER_01: And if you have just homogeneous geology with a hill, this is where geology and topography kind of interact.
28:46
SPEAKER_01: If you just have a massive hill or sort of a singular mountain, like a stratovolcano, or like an igneous massif, where there's just a big body of granite and it's a hill, it forms a topographic high, you're going to get a radio pattern because that granite is kind of homogenous throughout there.
29:02
SPEAKER_01: And what governs the way the water flows is the topography.
29:05
SPEAKER_01: And so you get a radial pattern around any hill that has kind of homogenous rocks within the hill itself.
29:11
SPEAKER_00: Yeah, good point.
29:12
SPEAKER_00: But then what happens when the slope flattens out, then the drainage pattern can change a great point.
29:18
SPEAKER_01: Great point.
29:19
SPEAKER_00: So dependent upon what the geology is away from that central high point, you'll get a new drainage pattern.
29:25
SPEAKER_00: So that's radial.
29:26
SPEAKER_00: That's a pretty simple one.
29:28
SPEAKER_00: I think so.
29:28
SPEAKER_00: The last one that we're going to cover, and I think this is the least common, but we do get this drainage pattern in some areas in the southwestern part of the United States, is a rectangular drainage pattern.
29:39
SPEAKER_00: Now, you question me, I'm like, all right, why are we talking about this last?
29:43
SPEAKER_00: Because a rectangular drainage pattern resembles from above, anyway, viewed from above, a trellis drainage pattern.
29:50
SPEAKER_00: So we have, in other words, rivers that are intersecting each other at roughly 90 degree angles.
29:56
SPEAKER_00: But that's really where the comparison starts and stops, because the the geology is totally different.
30:02
SPEAKER_00: So that's what it looks like.
30:04
SPEAKER_00: You have again these rivers and tributaries intersecting at 90 degrees.
30:09
SPEAKER_00: What's the geology that determines this, Jesse?
30:12
SPEAKER_01: The geology is again, it's sort of a flat area, so it's like dendritic, except there's structure to it.
30:17
SPEAKER_01: So this often occurs in flat-lying sedimentary rocks that have joints in them or fractures.
30:24
SPEAKER_01: And this happens a lot in like uh western Kentucky, Tennessee, where you have flat-lying sediments, but they're all jointed and faulted and fractured.
30:33
SPEAKER_01: And those jointing patterns are often 90 degrees.
30:36
SPEAKER_01: Chris, the the one interesting outcrop that we went to in undergrad in Michigan, which was like a day, the only real outcrop, a day's drive of rock from Holland, Michigan, was going to Grand Ledge on the Grand River and looking at sandstone that had been jointed.
30:51
SPEAKER_01: And we were measuring the jointing patterns.
30:53
SPEAKER_01: And the jointing patterns are all 90 degree intersections.
30:55
SPEAKER_01: So if water's flowing through that sandstone or flowing on top of that sandstone, it's going to follow those joints or those cracks or those weak areas in the rock.
31:03
SPEAKER_01: And I think, Chris, the way to differentiate this from trellis is trellis, you have down in the valleys that are parallel, you have bigger rivers in the valleys.
31:13
SPEAKER_01: And so all the tributaries are flowing kind of downwards towards these parallel main trunks.
31:19
SPEAKER_01: In rectangular, the main trunk will actually bend in the 90 degrees.
31:23
SPEAKER_01: So the main trunk will kind of be bending around, and the tributaries will also intersect at 90 degrees.
31:28
SPEAKER_01: But the main, I think of this as like the main trunk can be sort of bending 90 degrees and turning, and all of the corners are 90 degrees.
31:36
SPEAKER_01: All of the turns in the river system, it's not meandering, it's kind of bending at 90 degree angles.
31:41
SPEAKER_01: Different from trellis, where the main trunks are mostly parallel, mostly flowing straight and parallel.
31:46
SPEAKER_00: In addition to that, if you're looking at a topographic map at all, you can see the ridges and valleys, and that's going to be a trellis, whereas this rectangular pattern is relatively low relief, low, you know, difference between the high and the low elevation.
32:00
SPEAKER_00: It's basically flat.
32:01
SPEAKER_01: Yeah, basically flat.
32:03
SPEAKER_01: Yep, for the most part.
32:04
SPEAKER_00: Um all right.
32:05
SPEAKER_00: So, Jesse, we're gonna wrap it up with this.
32:07
SPEAKER_00: That you know, there are others that we could talk about, you know, and I'll I'll just mention a few.
32:12
SPEAKER_00: There's a deranged drainage pattern, there's a herringbone.
32:16
SPEAKER_00: I know I the yeah, it's and and there's a barbed drainage pattern.
32:20
SPEAKER_00: These are very niche drainage patterns.
32:22
SPEAKER_00: And so, you know, where do you start, where do you stop?
32:25
SPEAKER_00: We said, okay, let's do the top five, which I think we've covered most of the geography of the United States, then, in terms of the drainage patterns.
32:35
SPEAKER_01: Uh, most of the geography of the world.
32:37
SPEAKER_01: I mean, you know, a lot of it is covered by these types of patterns because they really are good examples of you have homogenous geology.
32:44
SPEAKER_01: Okay, it's dendritic, it's maybe rectangular.
32:47
SPEAKER_01: If you have a big hill or a volcano, you get radial.
32:50
SPEAKER_01: If you have tilted sediments, you get either trellis or annular, depending upon the structure of the tilted sediments, whether it's a dome or basin, or whether it's folded sediments that have been tilted up on edge and have long runways, like we described, of long valleys and ridges.
33:03
SPEAKER_01: So uh it covers most of the sort of geology that's exposed at the surface.
33:09
SPEAKER_01: It does.
33:09
SPEAKER_01: Uh that's why we hit these five.
33:11
SPEAKER_01: So super interesting stuff.
33:12
SPEAKER_01: I think you know, just when you're next looking at a topo map, you know, look at the river pattern and try and put it into one of these five categories and say, well, okay, how what does this tell me about the geology in the area that I live?
33:22
SPEAKER_01: I think it's a really interesting exercise to do.
33:24
SPEAKER_00: I think so as well.
33:26
SPEAKER_00: Hey, that's a wrap, Jesse.
33:27
SPEAKER_01: Drain patterns.
33:29
SPEAKER_01: We haven't finished our streams chapter yet for Camp Geo, but if you want to learn all the basics of geoscience up until the streams point, you can go to the first link in your show notes.
33:38
SPEAKER_01: That's geo.campcourses.com.
33:40
SPEAKER_01: There you can learn all the basics of geoscience with images, a key thing with the images.
33:44
SPEAKER_01: We're constantly uploading those images and updating those images as we speak.
33:48
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33:54
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33:58
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34:03
SPEAKER_01: Cheers.
34:04
SPEAKER_01: Peace.